1. Field of the Invention
The invention relates to a data processing apparatus including a CPU and a memory between which data transfer takes place through a data bus, particularly to a memory card, and more particularly to a data processing apparatus adapted to prevent the contents of data to be transferred on the data bus from being externally known.
2. Description of the Related Art
In general, a data processing apparatus such as a memory card internally including a CPU (a central processing unit) makes a slight difference in power consumption by the CPU for the processing of commands according to the type of command and data to be handled by each command. Therefore, the observation of the difference in power consumption as a change in a power current supplied to the data processing apparatus, for example, facilitates the analysis of operation of the CPU.
When the CPU manages and processes secret data in a memory, the secret data may be prone to leak out if the time required for the CPU to process the secret data is determined.
As mentioned above, a conventional data processing apparatus has the risk of the secret data being prone to leak out due to the difference in power consumption.